A particular problem with a typical integrated circuit comprising a plurality of circuit units including radio frequency units is the reduction of noise transmitted along power supply lines between the circuit units. For instance, digital circuit units generate noise signals that can seriously impair the performance of high-sensitivity units such as RF front end circuit units. This problem is prevalent in so-called System-on-Chip devices such as telecom transceivers. In a System-on-Chip transceiver, the RF circuit units may be subject to interference from digital circuit units, the interfering signals being transmitted on a supply line and through the substrate.
One known solution is to construct the RF circuits as fully differential circuits, which has the effect of reducing substrate and common-mode noise. In addition, driving the supply lines from a voltage regulator reduces supply noise. However, the latter solution is only partially effective for RF front-end circuit units since noise suppression using a voltage regulator tends to be confined within a frequency range of between, typically, 100 kHz and 1 MHz. Above 1 MHz, noise suppression tails off.
Fully differential circuits can extend the noise suppression frequency range according to the effective range of their common-mode control systems which are dependent on the frequency range of the common-mode control feedback in such systems. The effective bandwidth of a common-mode control circuit is typically slightly lower than its complete signal bandwidth. As a consequence, at the upper operating frequencies, interference still occurs as a result of supply line transmission.
It is an object of the invention to provide improved interference suppression in an integrated circuit having radio frequency circuit units.